A little experiment

Richard Bates said:

On Wed, 31 Mar 2004 21:35:03 GMT, in <2vprj1-
[email hidden]>, Simon Brooke

Quoted message said:

I strongly suspect that

(i) the inevitable internal errors in the computers
(e.g., occasional missed pulses) and

Would you think this could be minimalised or overcome
by ensuring the smallest practical gap between magnet
and sensor?

"Smallest practical gap" shouldn't be smallest gap to work
because there would be a danger of sensor slipping too close
where it could then click twice per rev.

But I really don't think missed or double pulses will be a
problem if magenet and sensor are well fixed. Epoxy resin on
magnet and soft rubber tape under sensor will do the job. It
still makes sense to position sensor in the middle of it's
working range, I think. Near the hub might be good as well,
as magent is travelling slower there.

I'm looking forward to the results. I bet the difference is
going to be more than most posters are predicting.

~PB

On Fri, 2 Apr 2004 16:59:34 +0100, in
<[email hidden]>, "Pete Biggs"

Quoted message said:

I'm looking forward to the results. I bet the difference is
going to be more than most posters are predicting.

Well I reckon it will be too, however the only way to be
certain is to experiment. Visualising the "ride through
puddle" scenario, I reckon that each intersection of the
front path with the rear adds a couple of centimetres, and I
reckin that slower speeds result in a higher difference.

Concerns about the wheels spinning when carrying the bike
are true but irrelevant since the bike+luggage will be so
Damn Heavy that I'll never carry it (and if do, the
computers will be turned off somehow).

I take on board what people have said about the errors being
greater than the actual answer. What would be most useful I
think is one of those clicking mechanical odometers
discussed in the Oval Chainring thread.

I also appreciate that tyre wear and pressure loss will be
different between front and rear tyres. Yes, the distance
calculated by the computer will be inaccurate but if I use
this figure to work out the number of wheel rev's then it
should be ok. It's just that I'll end up with an answer
using different units to what I originally decided (revs
instead of distance).

I think it is fair to assume that each identical computer
mounted in the same way will "miss" the same number of rev's
when expressed as a ratio to the actual number of revs. So
assuming the front wheel makes more rev's then the number of
missed rev's will also be higher, but still in proportion.
Perhaps if I did the trip twice (same route) and swapped the
computers over for the second journey I could validate the
result ;-)

I anticipate that my result will be greatly exagerated by
front panniers compared to an unloade bike.

General Note: Yes it is a very Sad Experiment (TM) but then
so was dropping stones off the tower of Pizza. And it sure
beats reality TV! And before anybody suggests that dropping
stones has some useful bearing into today's world, so will
this experiment...Anybody reading this who is an employer
offering a cycle-mileage to their employees, you will be
able to loss-adjust the discrepancy and save yourself four
pence a year in tax!

Love and amusement from Rich x

--
[email hidden] Personal Site: www.artybee.net (same
[censored], different layout) Sutton Brass :
www.suttonbrass.org.uk

Richard Bates said:

General Note: Yes it is a very Sad Experiment (TM) but
then so was dropping stones off the tower of Pizza.

I don't think it is so sad. If there does turn out to be a
substantial difference, we'll all be rigging up our
computers to our rear wheels, and thanking you for doing the
research for us!

Good luck on the tour.

~PB

On Fri, 2 Apr 2004 17:50:12 +0100, in
<[email hidden]>, "Pete Biggs"

Quoted message said:

Richard Bates said:

General Note: Yes it is a very Sad Experiment (TM) but
then so was dropping stones off the tower of Pizza.

I don't think it is so sad. If there does turn out to be a
substantial difference, we'll all be rigging up our
computers to our rear wheels, and thanking you for doing
the research for us!

And for my next experiment I'm going to measure the
difference between front-left and front-right wheels on a
recumbent when going anti-clockwise around the coast :-)

--
[email hidden] Personal Site: www.artybee.net (same
[censored], different layout) Sutton Brass :
www.suttonbrass.org.uk

Richard Bates said:

On Mon, 29 Mar 2004 12:47:11 +0100, in
<[email hidden]>, Richard
Bates <[email hidden]> wrote:

[excuse the top post but in this case it makes things
simpler]

As a follow up to my own post (below) in order to shed
some light on what I mean, let me explain.

When I cycle, although my front and rear wheel start and
end the same distance apart, I believe that the front
wheel actually travels via a more indirect route than the
rear i.e. it wobbles sideways more. This can be seen, as
another poster maintains, by riding through a puddle and
subsequently watching the trail made by the front and rear
wheels. The rear wheel, being the trailing wheel, appears
to resemble a straighter line than the front.

In my experience I wobble most when I'm travelling slowly &
uphill. Making up numbers, you may find that your front
wheel:back wheel distance ratio is
1.2:1 on uphills and 1.1:1 on flat stages & downhills. This
would prove your hypothesis that the distance travelled
by the front wheel may differ from the distance
travelled by the back wheel, without saying in absolute
terms how large that difference is likely to be.

Some cycle-computers have settings for 2 bikes so you could
use bike 1 to go uphill & bike 2 for downhill, but you'd
have to switch between them which would be a faff.

AC

Quoted message said:

I thought it would be amusing to measure the distance
travelled by each wheel independently.

Quoted message said:

Just had a mad idea whilst I was in the shower:

This year (May and June) I am doing a six week, very
indirect trip from John O'Groats to Land's End.

I thought it would be fun to measure the difference in
distance travelled by the front and rear wheels of my
bicycle.

I'm a knowledgaeable in scientific experiment construction
up to about A-Level standard. Apart from what is listed
below, can you think of any other important facts to make
it a valid setup?

1) Identical computers
2) Not wireless models (to avoid crosstalk)
3) Measure wheel circumferences independantly with bike
containing luggage with tyres pumped to my normal
pressure.

On 2/4/04 4:59 pm, in article [email hidden],

Pete Biggs said:

I'm looking forward to the results. I bet the difference
is going to be more than most posters are predicting.

My guess would be between 5-10%, ie outside the error range
but only just.

..d

Richard Bates said:

I also appreciate that tyre wear and pressure loss will be
different between front and rear tyres. Yes, the distance
calculated by the computer will be inaccurate but if I use
this figure to work out the number of wheel rev's then it
should be ok. It's just that I'll end up with an answer
using different units to what I originally decided (revs
instead of distance).

But the ratio of number of revs between front and rear
wheels is a bit of useless information. What you could do is
recalibrate the speedos every day, then I think the distance
would be pretty accurate.

How accurately do you think you can measure your wheels'
rolling circumference?

"Richard Bates" <[email hidden]> wrote

Quoted message said:

I also appreciate that tyre wear and pressure loss will be
different between front and rear tyres. Yes, the distance
calculated by the computer will be inaccurate but if I use
this figure to work out the number of wheel rev's then it
should be ok. It's just that I'll end up with an answer
using different units to what I originally decided (revs
instead of distance).

Am I missing something obvious here?

If one wheel loses pressure then because the radius is
smaller it'll do more revolutions than the other for the
same distance and it'll show a greater distance than you've
actually covered unless you input its new circumference
value into the computer. (My maths worked out that a 10mm
decrease in wheel radius corresponds to about a 3% increase
in recorded distance.)

So (taking both wheels travelling in dead straight line for
simplicity) if the computer on your original pressure wheel
shows your actual distance of 10km say, the one on the lower
pressure wheel will show a recorded distance of 10.3km. If
you divide the first of those by your roll out wheel
circumference of say, 2100mm you find it's done 4762
revolutions. What are you then going to divide the 10.3km
by? If you divide it by 2100mm you get 4905 revolutions but
that is still due to the fact that it's at lower pressure
than it should be and clearly doesn't tell you what you want
because in this example both wheels have travelled the same
distance. And dividing it by its new lower value roll out
circumference of (2037mm for a 10mm reduction of radius) you
get 5056 revolutions which just compounds the error.

Is that right or am I not getting what you mean?

Richard Bates said:

On Wed, 31 Mar 2004 21:35:03 GMT, in <2vprj1-
[email hidden]>, Simon Brooke
<[email hidden]> wrote:

Quoted message said:

Quoted message said:

(ii) variations in tyre diameter caused by wear and
pressure variation

Quoted message said:

This would affect the accuracy of the measured distance, it
is true, since an underinflated tyre will have a
circumference which does not equal what I have programmed
into the computer. However if I use the computer's distance
recording to calculate backwards and work out the number of
wheel revolutions front and rear (since afterall the
computer appears to be simply a rev counter and timer), I
will still end up with ratio F:R.

Not if the tyres deflate at different rates, wear at
different rates etc..

I think tyres introduce too many errors into this research
project. I think you should do it with solid wheels. All
these problems solved at one stroke.
--
Chris Malcolm [email hidden] +44 (0)131 651 3445 DoD #205
IPAB, Informatics, JCMB, King's Buildings, Edinburgh, EH9 3JZ, UK
["]http://www.dai.ed.ac.uk/homes/cam/]

On Sat, 3 Apr 2004 12:43:14 +0100,

AndyP said:

"Richard Bates" <[email hidden]> wrote

Quoted message said:

I also appreciate that tyre wear and pressure loss will
be different between front and rear tyres. Yes, the
distance calculated by the computer will be inaccurate
but if I use this figure to work out the number of wheel
rev's then it should be ok. It's just that I'll end up
with an answer using different units to what I originally
decided (revs instead of distance).

Am I missing something obvious here?

If one wheel loses pressure then because the radius is
smaller it'll do more revolutions than the other for the
same distance and it'll show a greater

<snip>

can you get steel belted tyres for bikes? That should
(practically) eliminate the problems with the circumference
changing other than through rubber wear (which should be
negligible)

Tim.

--
God said, "div D = rho, div B = 0, curl E = - @B/@t, curl H
= J + @D/@t," and there was light.

tjw.hn.orgtjw.hn.orgOpen ↗
locofungus.btinternet.co.uklocofungus.btinternet.co.ukOpen ↗

Pete Biggs said:

Richard Bates said:

General Note: Yes it is a very Sad Experiment (TM) but
then so was dropping stones off the tower of Pizza.

I don't think it is so sad. If there does turn out to be a
substantial difference, we'll all be rigging up our
computers to our rear wheels, and thanking you for doing
the research for us!

Until the more competitive amongst us realise this means
that we're not going half as fast as we thought we were 😉

AC

On Fri, 2 Apr 2004 17:50:12 +0100, "Pete Biggs"
<[email hidden]> wrote in message
<[email hidden]>:

Quoted message said:

I don't think it is so sad. If there does turn out to be a
substantial difference, we'll all be rigging up our
computers to our rear wheels, and thanking you for doing
the research for us!

Thinks: mine is already on the back wheel (Cateye Astrale).

--
Guy
===
May contain traces of irony. Contents liable to settle after
posting. chapmancentral.co.ukchapmancentral.co.ukOpen ↗

88% of helmet statistics are made up, 65% of them at
Washington University

On Sun, 4 Apr 2004 10:51:30 +0000 (UTC), in
<[email hidden]>, [email hidden] (Chris

Malcolm) said:

Not if the tyres deflate at different rates, wear at
different rates etc..

I think tyres introduce too many errors into this research
project. I think you should do it with solid wheels. All
these problems solved at one stroke.

I think 1000 miles on solid tyres would make my [censored] cheeks
travel different distances more than the two wheels.
--
Isn't it annoying when cyclingforums.com publish messages
that they haven't been granted permission to archive. In my
opinion it is as bad as software piracy.

Richard Bates <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

On Fri, 2 Apr 2004 17:50:12 +0100, in <[email hidden]-
berlin.de>, "Pete Biggs"

Quoted message said:

Richard Bates said:

General Note: Yes it is a very Sad Experiment (TM) but
then so was dropping stones off the tower of Pizza.

I don't think it is so sad. If there does turn out to be
a substantial difference, we'll all be rigging up our
computers to our rear wheels, and thanking you for doing
the research for us!

And for my next experiment I'm going to measure the
difference between front-left and front-right wheels on a
recumbent when going anti-clockwise around the coast :-)

My prediction is that the right wheel will travel exactly 8
x the inter-wheel-distance feet further than the left wheel
(assuming that you never get lost and find yourself doing
unintentional extra circles, as would happen if I tried).

Kit